Immunomorphometric indices in rats after administration of polyoxometalates

The impact of nanoparticles containing metal oxides may cause both increased proliferation and death of immunocompetent cells. Polyoxometalates (POMs) are nanoparticles containing iron (III) and molybdenum oxides. POMs are intended for targeted transport of drugs. Nanoparticles may produce effects that differ from those from a mixture of compounds within nanoparticles. The aim of the work is to investigate the effect of POMs and a mixture of POMs components (derivatives) on the morphometric parameters of the thymus, spleen, number of blood leukocytes and their precursors in bone marrow. The study was conducted in 25 mature male Wistar rats divided into 5 equal groups: animals in groups 1 and 2 were injected intramuscularly with POMs once and seven times, animals in groups 3 and 4 were injected with derivatives also once and seven times, the first group was left intact. A single dose of POMs or derivatives was 0.15 mg/100 g of body mass. We have evaluated cortical-medullar ratio in thymus and morphometric parameters of spleen (areas of stroma, white pulp, lymphoid follicles, and width of the mantle and marginal zones of lymphoid follicles). Based on the morphometric parameters, the quotients were calculated for the integral assessment of spleen morphometry: stromal-parenchymatous ratio (SPR), follicular coefficient (FC), and lymphoid coefficient (LC). The number of leukocytes and their fractions in peripheral blood, and the numbers of leukocyte precursors in bone marrow were determined. When comparing the parameters of rats treated with POMs and derivatives with appropriate indices of intact rats, the following results were obtained: we did not reveal any significant differences for the cortico-medullary ratios of thymus; increased SPR in group 3, like as of SPR, FC value, and the width of marginal zone in group 5. In groups 2-5, leukopenia was detected due to a deficiency of granulocytes. When derivatives were administered, the number of lymphocytes was also decreased in groups 4-5. Increased number of the bone marrow monocytic cells was detected in groups 3 and 5. Changes in peripheral immunopoietic organ, i.e., hyperplasia of spleen lymphatic tissues, was observed to more extent under the action of individual components of nanoparticles (derivatives) than after injection of POMs. The action of POMs and derivatives is less pronounced in central organs of the immune system, i.e., thymus and bone marrow. Compensation of the leukocyte deficiency in blood occurs, mainly, due to spleen leukopoiesis.